1. Field of the Invention
This invention relates to an exhaust gas purification system of an internal combustion engine having a catalyst or an adsorbent stored in a bypass exhaust gas passage (branched from the exhaust pipe and opened/closed by a switch-over valve) which adsorbs unburned components such as hydrocarbons (HC) of the exhaust gas generated by the engine to enhance exhaust gas purification. More particularly it relates to a system for controlling the operation of opening the switch-over valve at high engine speeds and loads to reduce noise and to introduce heated exhaust gas to burn cloggy material, such as soot away from the adsorbent, to prevent the adsorbent from deteriorating and regenerating the same.
2. Description of the Related Art
Internal combustion engines are ordinarily provided with a catalyst (a three-way catalytic converter) in the exhaust system which removes HC, NOx and CO components in the exhaust gas generated by the engine. However, when the engine is cold started, for example, and the catalyst is not activated, unburned components of the exhaust gas, in particular, unburned hydrocarbons (HC) are immediately released into the atmosphere. An exhaust gas purification system is therefore proposed, in which the exhaust pipe is branched out at a location downstream of the catalyst and the bypass exhaust gas passage is provided with a lightoff catalyst with an electric heater (for speedily activating the catalyst) or an adsorbent (a kind of catalyst made of a zeolite material or some similar materials) which adsorbs unburned components such as the HC content when the catalyst is not activated and desorbs the same to be recirculated into the engine intake system and burned again in the combustion chambers after the catalyst has been activated. A switch-over valve is provided at the branching point to regulate the introduction of exhaust gas into the bypass exhaust gas passage.
When the exhaust system is configured to have such a bypass exhaust gas passage branching from the exhaust pipe, the switch-over valve may sometimes chatter due to the pulsation of exhaust gas pressure and makes noise.
In order to solve this problem, Japanese Laid-Open Patent Application No. Hei 9 (1997)-72, 210 proposes a switch-over valve installed at the branching point of the exhaust pipe in such manner that, the disc of the valve is faced, at one surface, to the exhaust pipe through a first opening (exhaust pipe inner wall defining the main exhaust gas passage), and is faced, at the other surface, to the bypass exhaust gas passage through a second opening. In this prior art, the area of the second opening is configured to be smaller than that of the first opening in such a way that the difference between the pressures acting on the valve discs becomes less, thereby suppressing the valve disc chattering and hence, reducing noise due to the chattering.
However, this prior art is disadvantageous, in that it requires a complicated valve structure design to suppress the chattering.
Moreover, in this kind of internal combustion engine having the main exhaust gas passage and bypass exhaust gas passage, opening/closing of the intake and exhaust valves generates a pulsatory sound which may sometimes be amplified by the resonance in the main exhaust gas passage and the bypass exhaust gas passage. However, the aforesaid prior art does not cope with the reduction of this kind of noise.